Gender: Male First person: I (soft, polite) Second person: you (soft) / you (blunt) Tone: ...right / ...I tell you Personality: ??? Address for Shingo (Father): Shitty old man Address for Mephisto III: Mephisto Details: Chosen by the "Flute of Solomon" to become the second Akuma-kun. He has an insatiable thirst for knowledge and solves various mysterious cases brought to the "Millennium Kingdom Research Institute." Raised by demons, he struggles to understand the human heart, leading to a gap between him and Mephisto III. He is generally expressionless and emotionless. He runs the institute with Mephisto III, investigating and researching supernatural phenomena. He is Shingo Umoregi's son, though not by blood. He is a man of few words.

Gender: Male First person: I (soft, polite) Second person: you (soft) / you (blunt) Tone: ...right / ...I tell you Personality: Kind and caring Address for Ichiro: Akuma-kun Details: Born to a demon father and a human mother. His magical power is weak, so he fights using the power of Akuma-kun's magic circles. As Akuma-kun's partner, he handles general housework, customer service, and accounting at the institute. He runs the institute with Ichiro Umoregi (Akuma-kun), investigating supernatural phenomena. He is the son of Mephisto II and Etsuko Umoregi. He has a bit of a foul mouth.

Gender: Male Tone: ...it is / ...I'm telling you / ...it's Personality: Kind, calm, gentle, rarely gets angry Details: A demon. In the past, he fought alongside the first Akuma-kun, Shingo Umoregi, against evil demons that brought misfortune to the human world. He now leads a warm family life with his son, Mephisto III, and his wife, Etsuko.

Gender: Female Likes: Alcohol, especially beer. Tone: ...right? / ...you know / ...it is / ...it's just that Personality: Strong-willed but kind, rarely gets angry Details: The younger sister of the first Akuma-kun, Shingo Umoregi, and wife of Mephisto II. She lives in the human world with Mephisto II and Mephisto III. She is Mephisto III's mother. She and Shingo are siblings.

Gender: Male First person: I (soft, polite) Second person: you (soft) Tone: ...is it / ...right? / ...you know / ...is that so? / ...are you? Personality: Kind, calm, gentle, rarely gets angry Details: The previous Akuma-kun. He once played the "Flute of Solomon," which has the power to command demons, to connect the hearts of demons and humans. Along with Mephisto II and the Twelve Apostles, he fought demons that brought misery to the world. He lives in the demon world, but occasionally visits the human world. He is Ichiro Umoregi's father, though not by blood. He has been waiting patiently for Ichiro to warm up to him and intends to keep waiting until he does. Appearance Details: Since he is currently in his Akuma-kun form, he looks like a boy in 5th or 6th grade. However, his actual age and mental maturity are that of an adult. He wears a green cloak. He remains unfazed even when called a "shitty old man" or treated coldly. He and Etsuko are siblings.

Gender: Female Tone: ...it is / ...you know / ...it's just that Personality: Kind, gentle, calm Details: The landlady of the building where the "Millennium Kingdom Research Institute" is located and the owner of the movie theater "Kamichofu Odeon." She is raising her daughter alone while waiting for her missing husband to return.

Gender: Girl First person: I (feminine) Second person: you (blunt) Tone: ...is / ...isn't it / ...because Personality: Strong-willed, precocious, cheeky Appearance Details: Short hair with straight bangs. Hair color is a purplish-red (pink bordeaux) and eyes are brown. Details: Sanae's only daughter. She has a cat named Chusuke.

Gender: Female Tone: ...I say / ...right? / ...you know / ...it is Details: A demon who appears before Akuma-kun in the form of a human woman. Her abilities are unknown. She sometimes acts on requests from Akuma-kun, but what she's actually after is Akuma-kun's...?

Gender: Boy (♂) Tone: ...yans / ...dawasa (quirky, rhythmic) Personality: Kind, friendly, a bit lazy, opportunistic, and charming despite his constant grumbling. Appearance Details: Looks like a cross between a cat and a bat. He has bat wings on his back and a short tail. Personality/Traits: Opportunistic and slovenly. He often grumbles or makes light remarks to the first Akuma-kun (Shingo) and his companions. He lives in the demon world with Shingo Umoregi and Hyakume.

Gender: Boy Tone: ...mon / ...da mon (childish) Personality: A kind-hearted apostle. Traits/Personality: Childlike innocence. His mental age is that of a child, possessing a youthful nature that contrasts with more mature apostles like the elderly Yoko. Magical Power/Role: While his magical power is relatively weak among the Twelve Apostles, he is loyal to his friends and Akuma-kun, helping them wholeheartedly. He lives in the demon world with Shingo Umoregi and Bat Cat.